By Marilynn Larkin
NEW YORK (Reuters Health) – A recently developed smartphone app, DoseChecker, can rapidly calculate a patient’s optimal weekly hydroxychloroquine (Plaquenil) dose, thereby helping to avoid toxicity and eye injury, researchers say.
Hydroxychloroquine retinopathy is a potentially blinding condition for which there is no treatment. Therefore, primary prevention by appropriate dosing of hydroxychloroquine offers the best chance of minimizing the risk, according to Dr. Joan Miller of Massachusetts Eye and Ear, in Boston, and colleagues.
“This app provides a simple way for clinicians to both prescribe a dose of hydroxychloroquine that minimizes the risk of retinal toxicity and help their patients understand the rationale for the dosage regimen,” Dr. Miller said in an email to Reuters Health.
Study coauthor Dr. Elliot Perlman of the Rhode Island Eye Institute, in Providence, wrote the code for the app, and Massachusetts Eye and Ear is the Apple developer for it, the authors explain in a research letter in JAMA Ophthalmology, online January 4.
The app has been available free of charge in the App Store since September 2017.
The developers determined that the maximum daily dose, based on adjusted body weight, should be 5 (mg/kg/day) x ABW (kg).
The maximum daily dose, based on ideal body weight, is 6.5 (mg/kg/day) x IBW (kg).
The app does not distinguish between men and women because 95% of hydroxychloroquine retinopathy occurs in women, the authors state.
They note that the app takes two new approaches to hydroxychloroquine dosing:
-It uses both the ABW and the IBW methods instead of one or the other. It determines the maximum dose to avoid toxic effects and recommends the lower of the two as the safer dose.
-It uses an adjustable weekly dosing schedule. Since the drug is available only as a 200-mg tablet, the app suggests a total weekly dose using a combination of 200-mg and 400-mg doses to provide the highest therapeutic dose attainable without exceeding the toxic limit.
The prescribing physician enters the patient’s height and weight, touches the “calculate” button, and the recommended weekly dosing appears immediately. Dosing recommendations always fall within the approved drug labeling.
Dr. Miller said, “This is information that prescribing clinicians, especially primary care physicians and rheumatologists, should be made aware of. We are still brainstorming on how best to accomplish that and would welcome any ideas.”
“We have had at least one presentation at a rheumatology conference,” she noted. “It is our experience that rheumatologists believe Plaquenil to be such a safe drug – and it is in most respects – that they don’t worry about it and seem to think that retina complications are rare.”
“Although ophthalmologists are not usually the prescribing physicians,” she added, “the app would allow them to check the dosage regimen and make a recommendation to the prescribing rheumatologist or primary care provider.”
“We do believe that, in general, educating patients leads to better care and outcomes,” she continued. “Educating patients that there are eye concerns with Plaquenil, and that careful dosing, as well as screening and monitoring, matter is probably a good thing.”
“However,” she stressed, “it is the prescribing clinician who should use the app to determine the safe dosage and regimen.”
Dr. Sapna Gangaputra of the Vanderbilt Eye Institute, in Memphis, said in an email to Reuters Health, “We see several patients on Plaquenil, and as the paper states, the safest dose is calculated individually based on weight.”
“However,” she noted, “another very important aspect is the cumulative dose. Patients could be on safe dosing, but prolonged usage could contribute to toxicity.”
“The American Academy of Ophthalmology recommendations are annual eye checks after five years of use to assess for toxicity,” she added. “If the app could have built-in reminders to schedule eye appointments at those time points, that would be very useful.”
SOURCE: http://bit.ly/2FeOaMn
JAMA Ophthalmol 2018.
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